US 20070086538 A1 Abstract An improved interleaver design to fully explore the diversity of the MIMO OFDM systems provides higher diversity gain than usual. A method for wireless data communication using such interleaver design implements parsing a bit stream into multiple spatial data streams, interleaving the bits in each spatial data stream by performing bit circulation to increase diversity of the wireless system, and transmitting the bits of each spatial data stream.
Claims(12) 1. A method of data communication in a wireless system, comprising the steps of:
parsing a bit stream into multiple spatial data streams; interleaving the bits in a spatial data stream by steps including bit circulation to increase diversity of the wireless system; forming new data streams by bit combining after the bit circulation; and transmitting the bits of each newly formed spatial data stream. 2. The method of 3. The method of interleaving the bits according to IEEE 802.11a interleaving; splitting the bits in each data stream into multiple groups corresponding to subcarriers in a transmission symbol; performing a bit flip operation on the subcarriers; circulating the bits among the groups; and combining the bits for the different data streams to form a new bit sequence for transmission. 4. The method of 5. The method of 6. The method of 7. A wireless communication system, comprising:
a transmitter including:
a parser that parses a bit stream into multiple spatial data streams;
multiple interleavers corresponding to the multiple spatial data streams, wherein each of one or more interleavers performs interleaving of the bits in each of one or more spatial data streams by steps including bit circulation to increase diversity of the wireless system, the interleavers further forming new spatial data stream by bit combining after the bit circulation;
a modulator that transmits the bits of each newly formed spatial data stream; and
a receiver that receives and deinterleaves the transmitted bits.
8. The system of 9. The system of a splitter for splitting the bits in each data stream into multiple groups corresponding to subcarriers in a transmission symbol; a flipper for performing a bit flip operation on the subcarriers; a circulator for circulating the bits among the groups; and a combiner combining the bits for the different data streams to form a new bit sequence for transmission. 10. The system of 11. The system of 12. The system of Description The present invention relates generally to data communication, and more particularly, to data communication with transmission diversity using Orthogonal Frequency Division Multiplexing (OFDM) in multiple antenna channels. In wireless communication systems, antenna diversity plays an important role in increasing the system link robustness. OFDM is used as a modulation technique for transmitting digital data using radio frequency signals (RF). In OFDM, a radio signal is divided into multiple sub-signals that are transmitted simultaneously at different frequencies to a receiver. Each sub-signal travels within its own unique frequency range (sub-channel), which is modulated by the data. OFDM distributes the data over multiple channels, spaced apart at different frequencies. OFDM modulation is typically performed using a transform such as Fast Fourier Transform (FFT) process wherein bits of data are encoded in the frequency-domain onto sub-channels. As such, in the transmitter, an Inverse FFT (IFFT) is performed on the set of frequency channels to generate a time-domain OFDM symbol for transmission over a communication channel. The IFFT process converts the frequency-domain phase and amplitude data for each sub-channel into a block of time-domain samples which are converted to an analogue modulating signal for an RF modulator. In the receiver, the OFDM signals are processed by performing an FFT process on each symbol to convert the time-domain data into frequency-domain data, and the data is then decoded by examining the phase and amplitude of the sub-channels. Therefore, at the receiver the reverse process of the transmitter is implemented. Further, transmit antenna diversity schemes are used to improve the OFDM system reliability. Such transmit diversity schemes in OFDM systems are encoded in the frequency-domain as described. OFDM has been selected as the basis for the high speed wireless local area network (WLAN) standards by the IEEE standardization group. Referring to The system diagram in The present invention provides an improved interleaver design to fully explore the diversity of the MIMO OFDM systems. A bit flip and circulation interleaver design is provided for multiple encoder MIMO OFDM systems. Such an interleaver according to the present invention provides higher diversity gain than the conventional one. Accordingly, in one embodiment the present invention provides a system and method for wireless data communication, implementing the steps of: parsing a bit stream into multiple spatial data streams; interleaving the bits in each spatial data stream by performing bit circulation to increase diversity of the wireless system; and transmitting the bits of each spatial data stream. The steps of interleaving the bits in each spatial data stream further includes the steps of performing bit flipping. In one example, the steps of interleaving the bits include the steps of splitting the bits in each data stream into multiple groups corresponding to subcarriers in a transmission symbol, performing a bit flip operation on the subcarriers, circulating the bits among the groups, and combining the bits for the different data streams to form a new bit sequence for transmission. The bit flip operation further includes the steps of performing a bit flip operation on the subcarriers such that the bits on the same subcarrier are treated as a group which cannot be broken further down to smaller units. These and other features, aspects and advantages of the present invention will become understood with reference to the following description, appended claims and accompanying figures. FIGS. In one embodiment, the present invention provides an improved method interleaving for a MIMO OFDM system. The interleaving method improves exploration of the diversity of an MIMO OFDM system, providing higher diversity gain than usual. A bit flip and circulation interleaver design is provided for multiple encoder MIMO OFDM systems. Such an interleaver according to the present invention provides higher diversity gain than usual. Accordingly, in one embodiment the present invention provides a system and method for wireless data communication, implementing the steps of: parsing a bit stream into multiple spatial data streams; interleaving the bits in each spatial data stream; performing bit flipping; and performing bit circulation to increase diversity of the wireless system. Accordingly, an embodiment of an improved interleaver according to the present invention performs interleaving (e.g., IEEE 802.11a interleaving) on a data stream, and thereafter further performs a bit split into different groups by a bit flip and then a bit circulation, to complete the interleaver operation. In one example, the steps of interleaving the bits in an improved interleaver according to the present invention include the steps of: (1) splitting the bits in each data stream into multiple groups corresponding to subcarriers in a transmission symbol, (2) performing a bit flip operation on the subcarriers, (3) circulating the bits among the groups, and (4) combining the bits for the different data streams to form a new bit sequence for transmission. The bit flip operation further includes the steps of performing a bit flip operation on the subcarriers such that the bits on the same subcarrier are treated as a group which cannot be broken further down to smaller units. In this description, “bit flip and circulation” is the same as “bit flip and rotation”. As such, bit circulation and bit rotation are the same operations. In this example, for each data stream processing path For example, in a BPSK modulated OFDM transmitter, each subcarrier carries 1 bit and the bit-splitting will look like the following: Group Group In a 64 QAM modulated OFDM transmitter, where each subcarrier carries 6 bits, the bit-splitting will look like the following: Group Group For each data stream processing path The bit circulator Simulation results verify the improved performance of a MIMO system implementing an interleaving method described above (e.g.,
IEEE 802.11n channel models BNLOS and DNLOS have been used for simulation with the assumption of perfect synchronization, no RF impairment and perfect channel estimation. Further, an MMSE detector is used for data stream separation. FIGS. The above example interleaving implementations according to the present invention provide e.g. about 0.5 to 1 dB gain over the conventional interleaving methods. Although the description herein is based on two data streams in a two-antenna system, as those skilled in the art will recognize, the present invention is not limited to a specific number of transmission data streams and transmission antennas. With N transmission data streams, each stream can be split into N sub-streams for flip and rotation. The optimal flip method would depend on N, but using the same principle as described in the examples above. The optimal swap number also depends on N, but using the same principle as described in the examples above. The present invention has been described in considerable detail with reference to certain preferred versions thereof; however, other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein. Referenced by
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